At present, hand-held communication equipment has become more and more popular for its advantages such as free from the restriction of telephone line, handy portability and rapid connection. However, the radiation pollution brought by the hand-held communication equipment to the user shall not be ignored. Take a hand-held telephone set for example, when the user is having a call, the sound wave is converted into high-frequency electromagnetic wave by the hand-held telephone so as to send out electric signal. At the same time, relatively intensive high-frequency microwave radiation will occur in the surrounding space of the handset antenna. If the user's head part is exposed to such intense high frequency microwave radiation for long durations frequently, an injury to the user's head may be caused and result in pathological changes.
FIG. 1 is a diagram of electromagnetic radiation pattern of a conventional hand-held telephone antenna, which is used as an example to illustrate the radiation pollution of a hand-held telephone overshadowing the user's head.
The existing hand-held telephone antenna are usually divided into the following types: the ordinary rod type antenna, which is generally used in the communication equipment with microwave band with relatively shorter wavelength; inductively-loaded rod type antenna, which can be used in the communication equipment with relatively wider frequency band in which the length of the antenna is limited by the inductance for the purpose of shortening the antenna length so that it can be carried conveniently; pure inductance type antenna, used in mini and micro communication equipment, in which the antenna is minimized mainly for easy carrying; magnetic induction type antenna, used in single-section telescopic type hand-set, featuring a structure which is easy to carry and handy to use.
The electromagnetic waves transmitted by the above four types of antennae emit all around, as shown in FIG. 1, therefore the microwave radiation to the user will occur. Under the condition of the same power, the shorter the antenna is, the greater the transmitted power density will be, and consequently the severer the radiation to the user's head part will be. As it is specified explicitly in the safety and hygienic standards of environmental electromagnetic wave radiation published by the Health Ministry of the People's Republic of China that 40 mW/cm.sup.2 is the second-grade safety standard, the value exceeding this standard will have harmful influence on human body. Take the hand-held telephone for example, according to the test conducted by the China National Metrological Institute, when the transmitted power is 0.6 w, the electromagnetic power density around the antenna is 1100 to 2800 mW/cm.sup.2.